A DC/DC power converter receives an input direct current (DC) power, and converts it to a DC output power, typically exhibiting a different voltage than the input DC power. Control of the DC output power may be responsive to the output voltage or to the output current.
A boost converter, also known as a step-up converter, is a power converter with an output DC voltage greater than its input DC voltage. It is a class of switching-mode power supply containing at least a first electronically controlled switch, e.g. a transistor, at least a first energy storage element, e.g. an inductor, and an additional element such as a diode or a second electronically controlled switch. Typically, the first electronically controlled switch and diode, or second electronically controlled switch, are arranged between the inductor and the output, with current being alternately drawn to charge the inductor responsive to the first electronically controlled switch being closed, and passed to a load responsive to the first electronically controlled switch being open. The current goes through the diode or the second electronically controlled switch when it is passed to the load.
A buck converter, also known as a step-down converter, is a power converter with an output DC voltage less than its input DC voltage. It is a class of switching-mode power supply containing at least a third electronically controlled switch, e.g. a transistor, at least a second energy storage element, e.g. an inductor, and an additional element such as a diode or a fourth electronically controlled switch. Typically, the third electronically controlled switch and diode, or fourth electronically controlled switch, are arranged between the input DC power source and the inductor, with current being alternately drawn to charge the inductor through a load responsive to the third electronically controlled switch being closed, and continued to the load discharging the inductor responsive to the third electronically controlled switch being open. The diode or the fourth electronically controlled switch is in series with the inductor when the inductor is discharging to the load.
A classical or a cascaded buck-boost converter is a power converter with an output DC voltage which can be greater than or less than the input DC voltage. It is a class of switching-mode power supply containing at least two electronically controlled switches, at least one energy storage element, e.g. an inductor, and additional elements such as diodes and/or additional electronically controlled switches. Typically, each terminal of the inductor is coupled to at least one electronically controlled switch. The first electronically controlled switch, and optionally the second electronically controlled switch are controlled at either a fixed, or at a variable, switching frequency.
A flyback converter is a buck-boost converter with the inductor, acting as the energy storage element, split to form a transformer, so that the voltage ratios are multiplied with an additional advantage of isolation.
The above listing of power converters is meant to be illustrative of a number of topologies, however this is not meant to be limiting in any way.
Each of the DC/DC power converters is typically supplied with a feedback loop comprising an error amplifier so as to control either the output voltage or the output current to be maintained at a desired value, and at least one of the electronically controlled switches are controlled at either a fixed, or variable, switching frequency responsive to the error amplifier. In order to ensure stability in face of the feedback loop, the zero-crossing frequency, also known as the crossover frequency, of the error amplifier in open loop is typically set to be about 20-25% of the switching frequency. The term crossover frequency is meant to mean the frequency at which the error amplifier begins to exhibit a gain of less than 0 dB.
Many power converters provide the user with a settable switching frequency, typically by the selection of an external component value such as a resistor. The crossover frequency is typically fixed, and thus in order to ensure stability must be set at about 20-25% of the lowest switching frequency allowed. This is however disadvantageous, since in the event that the user has selected, by means of the external component value, a switching frequency in excess of the lowest switching frequency allowed, a higher crossover frequency which allows for a faster loop response time, thus providing faster recovery from changes in the input voltage or output load, provided that stability is ensured, can not be achieved. Thus, irrespective of the user selected switching frequency, the prior art typically supplies fixed crossover frequency.